Guide to Design of RCC Columns

Reinforced Concrete Columns

A column is a very important component in a structure. It is like the legs on which a structure stands. It is designed to resist axial and lateral forces and transfer them safely to the footings in the ground.

Columns support floors in a structure. Slabs and beams transfer the stresses to the columns. So, it is important to design strong columns.

Reinforced Cement Concrete Column Plan and Section

A column is defined as a compression member, the effective length of which exceeds three times the least lateral dimension. Compression members whose lengths do not exceed three times the least lateral dimension, may be made of plain concrete.

The axial load carrying capacity of a column is deduced from the formula

Please see the link for formulas to calculate axial loads in columns. I would recommend using advanced structural design software like ETabs or Staad Pro for design of structures. Column design does not depend only on axial loads, but also on many other factors. There are bending moments and tortional forces induced due to beam spans, wind loads, seismic loads, point loads and many other factors.

In this article, we are going to discuss in detail the basis of classification of columns and different types of reinforcement required for a certain type of column.

A column may be classified based on different criteria such as:

1. Based on shape

Rectangle

Square

Circular

Polygon

2. Based on slenderness ratio

The ratio of the effective length of a column to the least radius of gyration of its cross section is called the slenderness ratio.

Short RCC column, =< 10

Long RCC column, > 10

Short Steel column, =<50

Intermediate Steel column >50 & <200

Long Steel column >200

3. Based on type of loading

Axially loaded column

A column subjected to axial load and unaxial bending

A column subjected to axial load and biaxial bending

4. Based on pattern of lateral reinforcement

Tied RCC columns

Spiral RCC columns

Minimum eccentricity

Emin > l/500 + D/30 >20

Where, l = unsupported length of column in ‘mm’

D = lateral dimensions of column

Types of Reinforcements for columns and their requirements

Longitudinal Reinforcement

Minimum area of cross-section of longitudinal bars must be atleast 0.8% of gross section area of the column.

Maximum area of cross-section of longitudinal bars must not exceed 6% of the gross cross-section area of the column.

The bars should not be less than 12mm in diameter.

Minimum number of longitudinal bars must be four in rectangular column and 6 in circular column.

Spacing of longitudinal bars measures along the periphery of a column should not exceed 300mm.

Transverse reinforcement

It maybe in the form of lateral ties or spirals.

The diameter of the lateral ties should not be less than 1/4th of the diameter of the largest longitudinal bar and in no case less than 6mm.

The pitch of lateral ties should not exceed

Least lateral dimension

16 x diameter of longitudinal bars (small)

300mm

Helical Reinforcement

The diameter of helical bars should not be less than 1/4th the diameter of largest longitudinal and not less than 6mm.

Hello I have a site and have involved few architects to design the building. I need to know the structure design compatability. It will be kind of you if you provide any good reference who can save me even in earth quakes 🙂

There is no such thing as thumb rules…You must see a civil engineer if you want to get a structure designed. Structural engineering is a 4 year course. People work hard to become good civil engineers. If there were thumb rules for designing structures, we wouldn’t need Civil Engineers. Of course you must have found a contractor who would advise you that you dont need a civil engineer but trust me the building quality will be absolutely disastrous. You build a house once in a lifetime, invest wisely. Get experts involved. Your dream house should not look like a piece of trash. You want to live in a beautiful house and praise it every single day of your life.

my question is what is the meaning of cover from main bar ? if answer is center of bar to surface of concrete then where it is mention or if answer is face of main bar to surface of bar then where it is mention.

Structural design is never done on assumptions. It requires professional knowledge which comes only after you have studied and practiced engineering for a while. I suggest that you should stop assuming the column sizes with regards to plot area. The size of the column depends on the plan of the structure. It also depends on the height of the building.

hello,
i would like to ask if a RC column designed as 500mm x 700mm x 7000mm (H). After striked formwork, we found that the size casted was 500mm x 690mm x 7000mm (H), are there has any problem to column strength. concrete cover is 40mm from main bar to concrete surface are achieved during inspection.

wonderful knowledge u have …i am supposed to have put in more than 40 yrrs service …feel doubtful if i can do this .pl be writing …also suggest a good book for design of high rise building….we r not used to coputer design …how to do this c..more over in future only multy storeyed apts and offices will be in vogue…our mere concentration on small building is no good .of course the fundamentals r reqd… how the concreting is done for this with same labour who r nowadays used to max 6 or 7 storeys…crane is there..do they have the ladder system as u see in USA for plaster finish ..paint etc for high rause buildgs…hope u r the right person to answer my doubts ..if u do i will be grateful…u write excellent english …thanks…pl reply by mail….with best wishes…

….Can you please tell me,(a room 12’x14′,height 12′, in a normal house construction,ground floor and first floor,what should be the size of pillars?,can you please help me out,my house is under construction.

…sir/ma’am how about the close spacing of lateral ties of column near the beam-column joints any rule of thumb or code specs.? cause what i have only knew is that frm code: not to exceed 48 tie dia.,16 bar dia. or least dim.
cause as what i have always observed or seen in the actual there is always that close-spacing near the joints/supports. plz need reply, nd thank you & more powers.. .

we have a our own land development company where we buy huge parcels of land and divide it make sub divisions and sell those small piece of land to individual developers builders.we are only involved with the plotted development of the land.Generally after buying land we take necessary permissions and do the paper work for the residential or commercial development.now we provide compound walls gate and R.C.C. cement roads to our clients.i checked your website for simple compound wall footing plinth column beam structure basic knowledge but i get lost as there is so much in it and its difficult to find simple things like this..could you help me with this?thanks in advance

After reading what you do i thought it will be nice to do business with you,there is a piece of land in Cameroon were we intend to construct a tall building for commercial purpose and will like if you can help give me advice on what to do. Thanks in advance.